Hydrangeas (Hydrangea macrophylla)

These shrubs are widely grown in Australian gardens for their cool blue or pink flowers from summer to autumn. These deciduous shrubs can be grown as feature plants, as an informal hedge, or as a container or courtyard plant. They are well suited to that shaded part of the garden on the east or southern side of the house and are easy to grow from cuttings, which are taken in winter when plants are dormant.

Hydrangea macrophylla is known for its variable flower colour, which is a simple indicator of soil pH. Responding to the soil, hydrangeas flower blue in acid soils and pink in alkaline conditions. This variation is due to the availability of aluminium ions in the soil. The greater availability of aluminium in acid soils leads to increased blue colouration in the flowers.

There are two types of flower heads. Commonly grown are mophead varieties with large flower heads made up of a mass of small infertile flowers. Daintier and less familiar are lace-cap hydrangeas. These have a central cluster of tiny fertile flowers surrounded by a fringe of infertile flowers to give a lacy effect.

The large mophead flowers are produced on new wood, allowing flowers to be produced consistently throughout the summer season. In addition removing spent flower heads will encourage the formation of new flowers.

While hydrangeas are often sold as the species, there are many named varieties in sizes that range from under 1m to well over 2m in height and some of the newer varieties have double flowers or colourful stems. Check out your local hardware or garden centre for varieties to suit your location. Here are a few to get you thinking:

  • Hydrangeas (Hydrangea macrophylla) ‘Endless Summer’ A long-flowering variety new to Australia. It has large mophead blue or prink flowers (depending on the soil’s pH) which are produced on new wood. Remove spent flowers to get vibrant blooms from summer through to autumn.
  • Hydrangeas (Hydrangea macrophylla) ‘Blushing Bride’ From the same series as ‘Endless Summer’, it has stunning pure white mophead flowers that gradually fade to pale pink as the flowers mature. They make a great addition to any vase arrangement.
  • Hydrangeas (Hydrangea macrophylla) ‘Obsidian’ It is known for its abundant display of beautiful large fuchsia pink large mop top and lace cap flowers with stunning long black stems. A great variety for any garden as it can withstand frost and high temperatures.
  • Hydrangeas (Hydrangea macrophylla) ‘Broomstruck’ A beautiful repeat flowering hydrangea with a deep red mophead flower which can move to pink or blue depending on the pH of the soil. It will perform well given a part shade position in the garden.
  • Hydrangeas (Hydrangea macrophylla) ‘Tea Time Bicolour’ A unique bicolour variety with flowers with white borders and pink or blue flowers depending on the soil’s pH. A show stopper in any garden throughout the summer and early autumn, they prefer a shady position to look their best.
  • Hydrangeas (Hydrangea macrophylla) ‘Tuxedo Red’ A new stunning hydrangea for both foliage and flowers. It has striking dark purple/black, dense foliage against balls of red flowers which intensifies as the flowers mature. Planted in a shady position they will keep blooming throughout summer.

Growing conditions

Aspect Hydrangeas need a sheltered location with shade to part shade. In cool climates hydrangeas can tolerate full sun but will need extra watering. Protect hydrangeas from strong winds as their stems can be brittle.

Soil They grow best in a rich, fertile soil that holds moisture so dig in homemade compost or organic matter and/or Seasol Super Compost to prepare for planting. Reapply organic matter in winter as plants start to grow in spring and again in autumn after flowering to revitalise the soil. If growing In a container, use a premium potting mix such as Seasol Advanced Potting Mix.

Climate Hydrangeas grow in all areas except the tropics. In hot inland areas they require shade and additional water during summer. During periods of high heat they may need to be covered with shade cloth during the day. Remember to remove it in the cool of the evening.

General care

Watering Established plants are drought hardy but all grow and flower best with regular water. Water regularly (daily) if plants are in hot, dry or exposed conditions or if they are growing in containers. Hydrangeas wilt readily when moisture stressed and will need a good water to bounce back.

Feeding and mulching Hydrangeas are gross feeders which means they like a lot of nutrients to keep them growing and flowering, Feed throughout the seasons using a complete fertiliser for flowering plants such as Seasol plus Nutrients Roses & Flowers. Supplement feeding with a liquid fertiliser such as PowerFeed PRO SERIES for Roses & Flowers every 2 to 4 weeks. Plants in containers can be liquid fed every 2 to 4 weeks while they are growing and flowering. Apply PowerFeed PRO SERIES Roses & Flowers or PowerFeed All Purpose including Natives. Regular applications of Seasol will also assist drought hardiness and disease resistance.

Spread organic mulch such as sugarcane mulch, lucerne or pea straw to keep plants free of competing weeds and top up nutrients. For a deeper blue, apply hydrangea blueing tonic (available in garden centres) in spring (see directions on the container).

For pink or purple flowers, apply lime in autumn and spring to raise soil pH, or grow plants in a container with an alkaline potting mix.

Pruning Hydrangeas flower on new wood so prune in winter before new growth resumes. Cut back flowered stems to a pair of plump buds and remove any dead or very old stems, cutting off at the base. Hard pruning may reduce flowering but can be done to rejuvenate plants.

Propagate new plants from cuttings New plants can be propagated from cuttings in winter from old wood or in late spring from new soft wood.  For new softwood cuttings:

  1. Take a soft wood cutting about 10cm to 15cm long. Ensuring the top cutting ends above a node (where the new emerging leaves are) and below the node at the bottom of the cutting.
  2. Deadhead any flowers and remove all leaves except the top two, which are pruned in half to stop water evaporation.
  3. Dip in a suitable rooting hormone gel or powder (available from your local hardware or garden centre) and place the cutting in a pot in propagating media such as Seasol Seed Raising and Cutting Potting Mix so that a third of the bottom of the cutting is buried
  4. Water in well with Seasol and keep the media moist but not wet. Place in a position in the garden away from direct sunlight.
  5. Roots should emerge within a month to six weeks and be strong enough to plant into a larger pot.

Hardwood cuttings can also be taken in winter using the steps above.

Watch for Hydrangeas are generally unworried by pests or diseases but some may develop powdery mildew in late summer or autumn – prune off affected stems and clean up under plants once leaves are discarded. Scale may occasionally attack plants so spray with EarthCare Enviro Pest Oil insect spray. Do not spray when beneficial insects are around. Repeat applications may be necessary.